Future pulsed-power and power electronic capacitors will require dielectric materials ultimately having energy storage densities>30 J/cm3, with operating voltages>10 kV, and msec-μsec charge/discharge times with reliable operation near the dielectric breakdown limit. Importantly, at 2 J/cm3 and 0.2 J/cm3, respectively, the operating characteristics of current state-of-the-art pulsed power and power electronic capacitors, which utilize either ceramics or polymers as dielectric materials, remain significantly short of this goal. An order of magnitude improvement in energy density will require development of revolutionary new materials that substantially increase intrinsic dielectric energy densities while operating reliably near the dielectric breakdown limit. For simple linear response dielectric materials, energy density is defined in eq. 1, where ∈r is relative dielectric permittivity, E is the dielectric breakdown strength, and ∈0 is the vacuum permittivity. Generally, inorganic metal oxides exhibit high permittivities, however, they suffer from low breakdown fields. While organic materials (e.g., polymers) can provide high breakdown strengths, their generally low permittivities have limited their application.Ue=½∈r∈0E2  (1)
Recently, inorganic-polymer nanocomposite materials have attracted great interest due to their potential for high energy density. By integrating the complementary properties of their constituents, such materials can simultaneously derive high permittivity from the inorganic inclusions and high breakdown strength, mechanical flexibility, facile processability, light weight, and properties tunability (molecular weight, comonomer incorporation, thermal properties, etc.) from the polymer host matrix. Additionally, there are good reasons to believe that the large inclusion-matrix interfacial areas will afford higher polarization levels, dielectric response, and breakdown strength.
Although inorganic-polymer nanocomposites can be prepared via mechanical blending, solution mixing, in situ radical polymerization, and in situ nanoparticle synthesis, host-guest incompatibilities frequently result in nanoparticle aggregation and phase separation, detrimental to the electrical properties. Covalently grafting polymer chains to inorganic nanoparticle surfaces has also proven promising, leading to more effective dispersion and enhanced properties, however, such processes may not be cost-effective and nor easily scaled up.
Illustrating another approach, in the large-scale heterogeneous or slurry olefin polymerizations practiced on a huge industrial scale, SiO2 is generally used as the catalyst support. However, very large local hydraulic pressures arising from the growing polyolefin chains are known to effect extensive SiO2 particle fracture and lead to SiO2-polyolefin composites. As a result, there remains an on-going search in the art for an alternate route to inorganic-polymer nanocomposites, to better utilize the benefits and advantages afforded by such materials.